Method of operating UE in relation to release of sidelink RRC connection in wireless communication system

ABSTRACT

A method of operating a first user equipment (UE) in a wireless communication system is disclosed. The method includes establishing two or more PC5 radio resource control (RRC) connections with a second UE by the first UE, and releasing an RRC connection for which sidelink radio link failure (SL RLF) has been declared among the two or more PC5 RRC connections by the first UE. There is a PC5 unicast link associated with the PC5 RRC connection, and the PC5 unicast link for which the SL RLF has been declared and the PC5 RRC connection has been released is indicated by a PC5 link identifier (ID).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/929,934, filed on Nov. 3, 2019, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND Field

The present disclosure relates to a wireless communication system, andmore particularly, to a method and apparatus for operating a userequipment (UE) in relation to release of a sidelink radio resourcecontrol (RRC) connection.

Discussion of the Related Art

Wireless communication systems employ various radio access technologies(RATs) such as long term evolution (LTE), LTE-advanced (LTE-A), andwireless fidelity (WiFi). 5^(th) generation (5G) is also included in theRATs. Three key requirement areas of 5G are (1) enhanced mobilebroadband (eMBB), (2) massive machine type communication (mMTC), and (3)ultra-reliable and low latency communications (URLLC). Some use casesmay require multiple dimensions for optimization, while others may focusonly on one key performance indicator (KPI). 5G supports such diverseuse cases in a flexible and reliable way.

eMBB goes far beyond basic mobile Internet access and covers richinteractive work, media and entertainment applications in the cloud oraugmented reality (AR). Data is one of the key drivers for 5G and in the5G era, we may for the first time see no dedicated voice service. In 5G,voice is expected to be handled as an application program, simply usingdata connectivity provided by a communication system. The main driversfor an increased traffic volume are the increase in the size of contentand the number of applications requiring high data rates. Streamingservices (audio and video), interactive video, and mobile Internetconnectivity will continue to be used more broadly as more devicesconnect to the Internet. Many of these applications require always-onconnectivity to push real time information and notifications to users.Cloud storage and applications are rapidly increasing for mobilecommunication platforms. This is applicable for both work andentertainment. Cloud storage is one particular use case driving thegrowth of uplink data rates. 5G will also be used for remote work in thecloud which, when done with tactile interfaces, requires much lowerend-to-end latencies in order to maintain a good user experience.Entertainment, for example, cloud gaming and video streaming, is anotherkey driver for the increasing need for mobile broadband capacity.Entertainment will be very essential on smart phones and tabletseverywhere, including high mobility environments such as trains, carsand airplanes. Another use case is AR for entertainment and informationsearch, which requires very low latencies and significant instant datavolumes.

One of the most expected 5G use cases is the functionality of activelyconnecting embedded sensors in every field, that is, mMTC. It isexpected that there will be 20.4 billion potential Internet of things(IoT) devices by 2020. In industrial IoT, 5G is one of areas that playkey roles in enabling smart city, asset tracking, smart utility,agriculture, and security infrastructure.

URLLC includes services which will transform industries withultra-reliable/available, low latency links such as remote control ofcritical infrastructure and self-driving vehicles. The level ofreliability and latency are vital to smart-grid control, industrialautomation, robotics, drone control and coordination, and so on.

Now, multiple use cases will be described in detail.

5G may complement fiber-to-the home (FTTH) and cable-based broadband (ordata-over-cable service interface specifications (DOCSIS)) as a means ofproviding streams at data rates of hundreds of megabits per second togiga bits per second. Such a high speed is required for TV broadcasts ator above a resolution of 4K (6K, 8K, and higher) as well as virtualreality (VR) and AR. VR and AR applications mostly include immersivesport games. A special network configuration may be required for aspecific application program. For VR games, for example, game companiesmay have to integrate a core server with an edge network server of anetwork operator in order to minimize latency.

The automotive sector is expected to be a very important new driver for5G, with many use cases for mobile communications for vehicles. Forexample, entertainment for passengers requires simultaneous highcapacity and high mobility mobile broadband, because future users willexpect to continue their good quality connection independent of theirlocation and speed. Other use cases for the automotive sector are ARdashboards. These display overlay information on top of what a driver isseeing through the front window, identifying objects in the dark andtelling the driver about the distances and movements of the objects. Inthe future, wireless modules will enable communication between vehiclesthemselves, information exchange between vehicles and supportinginfrastructure and between vehicles and other connected devices (e.g.,those carried by pedestrians). Safety systems may guide drivers onalternative courses of action to allow them to drive more safely andlower the risks of accidents. The next stage will be remote-controlledor self-driving vehicles. These require very reliable, very fastcommunication between different self-driving vehicles and betweenvehicles and infrastructure. In the future, self-driving vehicles willexecute all driving activities, while drivers are focusing on trafficabnormality elusive to the vehicles themselves. The technicalrequirements for self-driving vehicles call for ultra-low latencies andultra-high reliability, increasing traffic safety to levels humanscannot achieve.

Smart cities and smart homes, often referred to as smart society, willbe embedded with dense wireless sensor networks. Distributed networks ofintelligent sensors will identify conditions for cost- andenergy-efficient maintenance of the city or home. A similar setup can bedone for each home, where temperature sensors, window and heatingcontrollers, burglar alarms, and home appliances are all connectedwirelessly. Many of these sensors are typically characterized by lowdata rate, low power, and low cost, but for example, real time highdefinition (HD) video may be required in some types of devices forsurveillance.

The consumption and distribution of energy, including heat or gas, isbecoming highly decentralized, creating the need for automated controlof a very distributed sensor network. A smart grid interconnects suchsensors, using digital information and communications technology togather and act on information. This information may include informationabout the behaviors of suppliers and consumers, allowing the smart gridto improve the efficiency, reliability, economics and sustainability ofthe production and distribution of fuels such as electricity in anautomated fashion. A smart grid may be seen as another sensor networkwith low delays.

The health sector has many applications that may benefit from mobilecommunications. Communications systems enable telemedicine, whichprovides clinical health care at a distance. It helps eliminate distancebarriers and may improve access to medical services that would often notbe consistently available in distant rural communities. It is also usedto save lives in critical care and emergency situations. Wireless sensornetworks based on mobile communication may provide remote monitoring andsensors for parameters such as heart rate and blood pressure.

Wireless and mobile communications are becoming increasingly importantfor industrial applications. Wires are expensive to install andmaintain, and the possibility of replacing cables with reconfigurablewireless links is a tempting opportunity for many industries. However,achieving this requires that the wireless connection works with asimilar delay, reliability and capacity as cables and that itsmanagement is simplified. Low delays and very low error probabilitiesare new requirements that need to be addressed with 5G

Finally, logistics and freight tracking are important use cases formobile communications that enable the tracking of inventory and packageswherever they are by using location-based information systems. Thelogistics and freight tracking use cases typically require lower datarates but need wide coverage and reliable location information.

A wireless communication system is a multiple access system thatsupports communication of multiple users by sharing available systemresources (a bandwidth, transmission power, etc.). Examples of multipleaccess systems include a CDMA system, an FDMA system, a TDMA system, anOFDMA system, an SC-FDMA system, and an MC-FDMA system.

Sidelink (SL) refers to a communication scheme in which a direct link isestablished between user equipments (UEs) and the UEs directly exchangevoice or data without intervention of a base station (BS). SL isconsidered as a solution of relieving the BS of the constraint ofrapidly growing data traffic.

Vehicle-to-everything (V2X) is a communication technology in which avehicle exchanges information with another vehicle, a pedestrian, andinfrastructure by wired/wireless communication. V2X may be categorizedinto four types: vehicle-to-vehicle (V2V), vehicle-to-infrastructure(V2I), vehicle-to-network (V2N), and vehicle-to-pedestrian (V2P). V2Xcommunication may be provided via a PC5 interface and/or a Uu interface.

As more and more communication devices demand larger communicationcapacities, there is a need for enhanced mobile broadband communicationrelative to existing RATs. Accordingly, a communication system is underdiscussion, for which services or UEs sensitive to reliability andlatency are considered. The next-generation RAT in which eMBB, MTC, andURLLC are considered is referred to as new RAT or NR. In NR, V2Xcommunication may also be supported.

FIG. 1 is a diagram illustrating V2X communication based on pre-NR RATand V2X communication based on NR in comparison.

For V2X communication, a technique of providing safety service based onV2X messages such as basic safety message (BSM), cooperative awarenessmessage (CAM), and decentralized environmental notification message(DENM) was mainly discussed in the pre-NR RAT. The V2X message mayinclude location information, dynamic information, and attributeinformation. For example, a UE may transmit a CAM of a periodic messagetype and/or a DENM of an event-triggered type to another UE.

For example, the CAM may include basic vehicle information includingdynamic state information such as a direction and a speed, vehiclestatic data such as dimensions, an external lighting state, pathdetails, and so on. For example, the UE may broadcast the CAM which mayhave a latency less than 100 ms. For example, when an unexpectedincident occurs, such as breakage or an accident of a vehicle, the UEmay generate the DENM and transmit the DENM to another UE. For example,all vehicles within the transmission range of the UE may receive the CAMand/or the DENM. In this case, the DENM may have priority over the CAM.

In relation to V2X communication, various V2X scenarios are presented inNR. For example, the V2X scenarios include vehicle platooning, advanceddriving, extended sensors, and remote driving.

For example, vehicles may be dynamically grouped and travel togetherbased on vehicle platooning. For example, to perform platoon operationsbased on vehicle platooning, the vehicles of the group may receiveperiodic data from a leading vehicle. For example, the vehicles of thegroup may widen or narrow their gaps based on the periodic data.

For example, a vehicle may be semi-automated or full-automated based onadvanced driving. For example, each vehicle may adjust a trajectory ormaneuvering based on data obtained from a nearby vehicle and/or a nearbylogical entity. For example, each vehicle may also share a dividingintention with nearby vehicles.

Based on extended sensors, for example, raw or processed data obtainedthrough local sensor or live video data may be exchanged betweenvehicles, logical entities, terminals of pedestrians and/or V2Xapplication servers. Accordingly, a vehicle may perceive an advancedenvironment relative to an environment perceivable by its sensor.

Based on remote driving, for example, a remote driver or a V2Xapplication may operate or control a remote vehicle on behalf of aperson incapable of driving or in a dangerous environment. For example,when a path may be predicted as in public transportation, cloudcomputing-based driving may be used in operating or controlling theremote vehicle. For example, access to a cloud-based back-end serviceplatform may also be used for remote driving.

A scheme of specifying service requirements for various V2X scenariosincluding vehicle platooning, advanced driving, extended sensors, andremote driving is under discussion in NR-based V2X communication.

SUMMARY

Provided is a method of identifying a PC5 unicast link, when a radioresource control (RRC) connection associated with the PC5 unicast linkis released due to radio link failure (RLF) declaration at a userequipment (UE) having a plurality of PC5 RRC connections.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments of the disclosure.

According to an embodiment of the present disclosure, a method ofoperating a first UE in a wireless communication system includesestablishing two or more PC5 RRC connections with a second UE by thefirst UE, and releasing an RRC connection for which SL RLF has beendeclared among the two or more PC5 RRC connections by the first UE.There is a PC5 unicast link associated with the PC5 RRC connection, andthe PC5 unicast link for which the SL RLF has been declared and the PC5RRC connection has been released is indicated by a PC5 link identifier(ID)

According to another embodiment of the present disclosure, a first UE ina wireless communication system includes at least one processor, and atleast one computer memory operatively coupled to the at least oneprocessor and storing instructions which when executed, cause the atleast one process to perform operations. The operations includeestablishing two or more PC5 connections with a second UE by the firstUE, and releasing an RRC connection for which SL RLF has been declaredamong the two or more PC5 RRC connections by the first UE. There is aPC5 unicast link associated with the PC5 RRC connection, and the PC5unicast link for which the SL RLF has been declared and the PC5 RRCconnection has been released is indicated by a PC5 unicast link ID.

According to another embodiment of the present disclosure, a processorfor performing operations for a UE in a wireless communication system isprovided. The operations include establishing two or more PC5 RRCconnections with a second UE by a first UE, and releasing an RRCconnection for which SL RLF has been declared among the two or more PC5RRC connections by the first UE. There is a PC5 unicast link associatedwith the PC5 RRC connection, and the PC5 unicast link for which the SLRLF has been declared and the PC5 RRC connection has been released isindicated by a PC5 unicast link ID.

According to another embodiment of the present disclosure, acomputer-readable storage medium stores at least one computer program,and the at least one computer program includes instructions which whenexecuted by at least one processor, cause the at least one processor toperform operations for a UE. The operations includes establishing two ormore PC5 RRC connections with a second UE by a first UE, and releasingan RRC connection for which SL RLF has been declared among the two ormore PC5 RRC connections by the first UE. There is a PC5 unicast linkassociated with the PC5 RRC connection, and the PC5 unicast link forwhich the SL RLF has been declared and the PC5 RRC connection has beenreleased is indicated by a PC5 unicast link ID.

The first UE may transmit, to a base station (BS), information relatedto the PC5 unicast link for which the SL RLF has been declared and thePC5 RRC connection has been released.

When another PC5 RRC connection is released for a reason other than SLRLF among the two or more PC5 RRC connections, the first UE maytransmit, to the B S, information related to a PC5 unicast linkassociated with the PC5 RRC connection.

The reason other than SL RLF may include one or more of PC5 RRC resumefailure, PC5 RRC connection failure, PC5 RRC suspension, load balancingrequired for PC5 interface, mismatch between UE capabilities of UEs, andaccess stratum (AS) layer configuration failure between UEs.

When another PC5 RRC connection is released for a reason other than SLRLF among the two or more PC5 RRC connections, the first UE maytransmit, to a higher layer, information related to a PC5 unicast linkassociated with the PC5 RRC connection.

The method may further include transmitting a signal based on at leastone of the two or more PC5 RRC connections by the first UE.

The PC5 unicast link ID may be transmitted from an access stratum (AS)layer of the first UE to a vehicle-to-everything (V2X) layer of thefirst UE.

The V2X layer may release the PC5 unicast link indicated by the PC5unicast link ID.

The PC5 unicast link may be related to the PC5 RRC connection releasedby the SL RLF.

An AS layer of the first UE may indicate to a V2X layer of the first UEthat the PC5 RRC connection has been released based on the SL RLF

The first UE may communicate with at least one of another UE, a UE or BSrelated to an autonomous driving vehicle, or a network.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a diagram comparing vehicle-to-everything (V2X) communicationbased on pre-new radio access technology (pre-NR) with V2X communicationbased on NR;

FIG. 2 is a diagram illustrating the structure of a long term evolution(LTE) system according to an embodiment of the present disclosure;

FIGS. 3A and 3B are diagrams illustrating user-plane and control-planeradio protocol architectures according to an embodiment of the presentdisclosure;

FIG. 4 is a diagram illustrating the structure of an NR system accordingto an embodiment of the present disclosure;

FIG. 5 is a diagram illustrating functional split between a nextgeneration radio access network (NG-RAN) and a 5^(th) generation corenetwork (5GC) according to an embodiment of the present disclosure;

FIG. 6 is a diagram illustrating the structure of an NR radio frame towhich embodiment(s) of the present disclosure is applicable;

FIG. 7 is a diagram illustrating a slot structure of an NR frameaccording to an embodiment of the present disclosure;

FIGS. 8A and 8B are diagrams illustrating radio protocol architecturesfor sidelink (SL) communication according to an embodiment of thepresent disclosure;

FIGS. 9A and 9B are diagrams illustrating radio protocol architecturesfor SL communication according to an embodiment of the presentdisclosure;

FIGS. 10A and 10B are diagrams illustrating the structure of a secondarysynchronization signal block (S-SSB) in a normal cyclic prefix (NCP)case according to an embodiment of the present disclosure;

FIGS. 11, 12, 13, 14, and 15 are diagrams illustrating embodiment(s);and

FIGS. 16, 17, 18, 19, 20, 21, and 22 are diagrams illustrating variousdevices to which embodiment(s) is applicable.

DETAILED DESCRIPTION

In various embodiments of the present disclosure, “I” and “,” should beinterpreted as “and/or”. For example, “A/B” may mean “A and/or B”.Further, “A, B” may mean “A and/or B”. Further, “AB/C” may mean “atleast one of A, B and/or C”. Further, “A, B, C” may mean “at least oneof A, B and/or C”.

In various embodiments of the present disclosure, “or” should beinterpreted as “and/or”. For example, “A or B” may include “only A”,“only B”, and/or “both A and B”. In other words, “or” should beinterpreted as “additionally or alternatively”.

Techniques described herein may be used in various wireless accesssystems such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-frequencydivision multiple access (SC-FDMA), and so on. CDMA may be implementedas a radio technology such as universal terrestrial radio access (UTRA)or CDMA2000. TDMA may be implemented as a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA maybe implemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, evolved-UTRA (E-UTRA), or the like. IEEE802.16m is an evolution of IEEE 802.16e, offering backward compatibilitywith an IRRR 802.16e-based system. UTRA is a part of universal mobiletelecommunications system (UMTS). 3^(rd) generation partnership project(3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS)using evolved UTRA (E-UTRA). 3GPP LTE employs OFDMA for downlink (DL)and SC-FDMA for uplink (UL). LTE-advanced (LTE-A) is an evolution of3GPP LTE.

A successor to LTE-A, 5^(th) generation (5G) new radio access technology(NR) is a new clean-state mobile communication system characterized byhigh performance, low latency, and high availability. 5G NR may use allavailable spectral resources including a low frequency band below 1 GHz,an intermediate frequency band between 1 GHz and 10 GHz, and a highfrequency (millimeter) band of 24 GHz or above.

While the following description is given mainly in the context of LTE-Aor 5G NR for the clarity of description, the technical idea of anembodiment of the present disclosure is not limited thereto.

FIG. 2 illustrates the structure of an LTE system according to anembodiment of the present disclosure. This may also be called an evolvedUMTS terrestrial radio access network (E-UTRAN) or LTE/LTE-A system.

Referring to FIG. 2 , the E-UTRAN includes evolved Node Bs (eNBs) 20which provide a control plane and a user plane to UEs 10. A UE 10 may befixed or mobile, and may also be referred to as a mobile station (MS),user terminal (UT), subscriber station (SS), mobile terminal (MT), orwireless device. An eNB 20 is a fixed station communication with the UE10 and may also be referred to as a base station (BS), a basetransceiver system (BTS), or an access point.

eNBs 20 may be connected to each other via an X2 interface. An eNB 20 isconnected to an evolved packet core (EPC) 39 via an S1 interface. Morespecifically, the eNB 20 is connected to a mobility management entity(MME) via an S1-MME interface and to a serving gateway (S-GW) via anS1-U interface.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information or capability information aboutUEs, which are mainly used for mobility management of the UEs. The S-GWis a gateway having the E-UTRAN as an end point, and the P-GW is agateway having a packet data network (PDN) as an end point.

Based on the lowest three layers of the open system interconnection(OSI) reference model known in communication systems, the radio protocolstack between a UE and a network may be divided into Layer 1 (L1), Layer2 (L2) and Layer 3 (L3). These layers are defined in pairs between a UEand an Evolved UTRAN (E-UTRAN), for data transmission via the Uuinterface. The physical (PHY) layer at L1 provides an informationtransfer service on physical channels. The radio resource control (RRC)layer at L3 functions to control radio resources between the UE and thenetwork. For this purpose, the RRC layer exchanges RRC messages betweenthe UE and an eNB.

FIG. 3A illustrates a user-plane radio protocol architecture accordingto an embodiment of the disclosure.

FIG. 3B illustrates a control-plane radio protocol architectureaccording to an embodiment of the disclosure. A user plane is a protocolstack for user data transmission, and a control plane is a protocolstack for control signal transmission.

Referring to FIGS. 3A and 3B, the PHY layer provides an informationtransfer service to its higher layer on physical channels. The PHY layeris connected to the medium access control (MAC) layer through transportchannels and data is transferred between the MAC layer and the PHY layeron the transport channels. The transport channels are divided accordingto features with which data is transmitted via a radio interface.

Data is transmitted on physical channels between different PHY layers,that is, the PHY layers of a transmitter and a receiver. The physicalchannels may be modulated in orthogonal frequency division multiplexing(OFDM) and use time and frequencies as radio resources.

The MAC layer provides services to a higher layer, radio link control(RLC) on logical channels. The MAC layer provides a function of mappingfrom a plurality of logical channels to a plurality of transportchannels. Further, the MAC layer provides a logical channel multiplexingfunction by mapping a plurality of logical channels to a singletransport channel. A MAC sublayer provides a data transmission serviceon the logical channels.

The RLC layer performs concatenation, segmentation, and reassembly forRLC serving data units (SDUs). In order to guarantee various quality ofservice (QoS) requirements of each radio bearer (RB), the RLC layerprovides three operation modes, transparent mode (TM), unacknowledgedmode (UM), and acknowledged Mode (AM). An AM RLC provides errorcorrection through automatic repeat request (ARQ).

The RRC layer is defined only in the control plane and controls logicalchannels, transport channels, and physical channels in relation toconfiguration, reconfiguration, and release of RBs. An RB refers to alogical path provided by L1 (the PHY layer) and L2 (the MAC layer, theRLC layer, and the packet data convergence protocol (PDCP) layer), fordata transmission between the UE and the network.

The user-plane functions of the PDCP layer include user datatransmission, header compression, and ciphering. The control-planefunctions of the PDCP layer include control-plane data transmission andciphering/integrity protection.

RB establishment amounts to a process of defining radio protocol layersand channel features and configuring specific parameters and operationmethods in order to provide a specific service. RBs may be classifiedinto two types, signaling radio bearer (SRB) and data radio bearer(DRB). The SRB is used as a path in which an RRC message is transmittedon the control plane, whereas the DRB is used as a path in which userdata is transmitted on the user plane.

Once an RRC connection is established between the RRC layer of the UEand the RRC layer of the E-UTRAN, the UE is placed in RRC CONNECTEDstate, and otherwise, the UE is placed in RRC IDLE state. In NR, RRCINACTIVE state is additionally defined. A UE in the RRC INACTIVE statemay maintain a connection to a core network, while releasing aconnection from an eNB.

DL transport channels carrying data from the network to the UE include abroadcast channel (BCH) on which system information is transmitted and aDL shared channel (DL SCH) on which user traffic or a control message istransmitted. Traffic or a control message of a DL multicast or broadcastservice may be transmitted on the DL-SCH or a DL multicast channel (DLMCH). UL transport channels carrying data from the UE to the networkinclude a random access channel (RACH) on which an initial controlmessage is transmitted and an UL shared channel (UL SCH) on which usertraffic or a control message is transmitted.

The logical channels which are above and mapped to the transportchannels include a broadcast control channel (BCCH), a paging controlchannel (PCCH), a common control channel (CCCH), a multicast controlchannel (MCCH), and a multicast traffic channel (MTCH).

A physical channel includes a plurality of OFDM symbol in the timedomain by a plurality of subcarriers in the frequency domain. Onesubframe includes a plurality of OFDM symbols in the time domain. An RBis a resource allocation unit defined by a plurality of OFDM symbols bya plurality of subcarriers. Further, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) in acorresponding subframe for a physical DL control channel (PDCCH), thatis, an L1/L2 control channel. A transmission time interval (TTI) is aunit time for subframe transmission.

FIG. 4 illustrates the structure of an NR system according to anembodiment of the present disclosure.

Referring to FIG. 4 , a next generation radio access network (NG-RAN)may include a next generation Node B (gNB) and/or an eNB, which providesuser-plane and control-plane protocol termination to a UE. In FIG. 4 ,the NG-RAN is shown as including only gNBs, by way of example. A gNB andan eNB are connected to each other via an Xn interface. The gNB and theeNB are connected to a 5G core network (5GC) via an NG interface. Morespecifically, the gNB and the eNB are connected to an access andmobility management function (AMF) via an NG-C interface and to a userplane function (UPF) via an NG-U interface.

FIG. 5 illustrates functional split between the NG-RAN and the 5GCaccording to an embodiment of the present disclosure.

Referring to FIG. 5 , a gNB may provide functions including inter-cellradio resource management (RRM), radio admission control, measurementconfiguration and provision, and dynamic resource allocation. The AMFmay provide functions such as non-access stratum (NAS) security andidle-state mobility processing. The UPF may provide functions includingmobility anchoring and protocol data unit (PDU) processing. A sessionmanagement function (SMF) may provide functions including UE Internetprotocol (IP) address allocation and PDU session control.

FIG. 6 illustrates a radio frame structure in NR, to which embodiment(s)of the present disclosure is applicable.

Referring to FIG. 6 , a radio frame may be used for UL transmission andDL transmission in NR. A radio frame is 10 ms in length, and may bedefined by two 5-ms half-frames. An HF may include five 1-ms subframes.A subframe may be divided into one or more slots, and the number ofslots in an SF may be determined according to a subcarrier spacing(SCS). Each slot may include 12 or 14 OFDM(A) symbols according to acyclic prefix (CP).

In a normal CP (NCP) case, each slot may include 14 symbols, whereas inan extended CP (ECP) case, each slot may include 12 symbols. Herein, asymbol may be an OFDM symbol (or CP-OFDM symbol) or an SC-FDMA symbol(or DFT-s-OFDM symbol).

[Table 1] below lists the number of symbols per slot N^(slot) _(symb),the number of slots per frame N^(frame,u) _(slot), and the number ofslots per subframe N^(subfrme,u) _(slot) according to an SCSconfiguration μ in the NCP case.

TABLE 1 SCS (15*2u) N^(slot) _(symb) N^(frame, u) _(slot)N^(subframe, u) _(slot) 15 kHz 14 10 1 (u = 0) 30 kHz 14 20 2 (u = 1) 60kHz 14 40 4 (u = 2) 120 kHz  14 80 8 (u = 3) 240 kHz  14 160 16 (u = 4)

[Table 2] below lists the number of symbols per slot, the number ofslots per frame, and the number of slots per subframe according to anSCS in the ECP case.

TABLE 2 SCS (15*2{circumflex over ( )}u) N^(slot) _(symb) N^(frame, u)_(slot) N^(subframe, u) _(slot) 60 KHz 12 40 4 (u = 2)

In the NR system, different OFDM(A) numerologies (e.g., SCSs, CPlengths, and so on) may be configured for a plurality of cellsaggregated for one UE. Accordingly, the (absolute time) duration of atime resource including the same number of symbols (e.g., a subframe,slot, or TTI) (collectively referred to as a time unit (TU) forconvenience) may be configured to be different for the aggregated cells.

In NR, various numerologies or SCSs may be supported to support various5G services. For example, with an SCS of 15 kHz, a wide area intraditional cellular bands may be supported, while with an SCS of 30kHz/60 kHz, a dense urban area, a lower latency, and a wide carrierbandwidth may be supported. With an SCS of 60 kHz or higher, a bandwidthlarger than 24.25 GHz may be supported to overcome phase noise.

An NR frequency band may be defined by two types of frequency ranges,FR1 and FR2. The numerals in each frequency range may be changed. Forexample, the two types of frequency ranges may be given in [Table 3]. Inthe NR system, FR1 may be a “sub 6 GHz range” and FR2 may be an “above 6GHz range” called millimeter wave (mmW).

TABLE 3 Frequency Corresponding Subcarrier Range designation frequencyrange Spacing (SCS) FR1  450 MHz-6000 MHz 15, 30, 60 kHz FR2 24250MHz-52600 MHz 60, 120, 240 kHz

As mentioned above, the numerals in a frequency range may be changed inthe NR system. For example, FR1 may range from 410 MHz to 7125 MHz aslisted in [Table 4]. That is, FR1 may include a frequency band of 6 GHz(or 5850, 5900, and 5925 MHz) or above. For example, the frequency bandof 6 GHz (or 5850, 5900, and 5925 MHz) or above may include anunlicensed band. The unlicensed band may be used for various purposes,for example, vehicle communication (e.g., autonomous driving).

TABLE 4 Frequency Corresponding Subcarrier Range designation frequencyrange Spacing (SCS) FR1  410 MHz-7125 MHz 15, 30, 60 kHz FR2 24250MHz-52600 MHz 60, 120, 240 kHz

FIG. 7 illustrates a slot structure in an NR frame according to anembodiment of the present disclosure.

Referring to FIG. 7 , a slot includes a plurality of symbols in the timedomain. For example, one slot may include 14 symbols in an NCP case and12 symbols in an ECP case. Alternatively, one slot may include 7 symbolsin an NCP case and 6 symbols in an ECP case.

A carrier includes a plurality of subcarriers in the frequency domain.An RB may be defined by a plurality of (e.g., 12) consecutivesubcarriers in the frequency domain. A bandwidth part (BWP) may bedefined by a plurality of consecutive (physical) RBs ((P)RBs) in thefrequency domain and correspond to one numerology (e.g., SCS, CP length,or the like). A carrier may include up to N (e.g., 5) BWPs. Datacommunication may be conducted in an activated BWP. Each element may bereferred to as a resource element (RE) in a resource grid, to which onecomplex symbol may be mapped.

A radio interface between UEs or a radio interface between a UE and anetwork may include L1, L2, and L3. In various embodiments of thepresent disclosure, L1 may refer to the PHY layer. For example, L2 mayrefer to at least one of the MAC layer, the RLC layer, the PDCH layer,or the SDAP layer. For example, L3 may refer to the RRC layer.

Now, a description will be given of sidelink (SL) communication.

FIGS. 8A and 8B illustrate a radio protocol architecture for SLcommunication according to an embodiment of the present disclosure.Specifically, FIG. 8A illustrates a user-plane protocol stack in LTE,and FIG. 8B illustrates a control-plane protocol stack in LTE.

FIGS. 9A and 9B illustrate a radio protocol architecture for SLcommunication according to an embodiment of the present disclosure.Specifically, FIG. 9A illustrates a user-plane protocol stack in NR, andFIG. 9B illustrates a control-plane protocol stack in NR. A descriptionwill be given of SL resource allocation.

Resource allocation in SL will be described below.

FIGS. 10A and 10B illustrate a procedure of performing V2X or SLcommunication according to a transmission mode in a UE according to anembodiment of the present disclosure. In various embodiments of thepresent disclosure, a transmission mode may also be referred to as amode or a resource allocation mode. For the convenience of description,a transmission mode in LTE may be referred to as an LTE transmissionmode, and a transmission mode in NR may be referred to as an NR resourceallocation mode.

For example, FIG. 10A illustrates a UE operation related to LTEtransmission mode 1 or LTE transmission mode 3. Alternatively, forexample, FIG. 10A illustrates a UE operation related to NR resourceallocation mode 1. For example, LTE transmission mode 1 may be appliedto general SL communication, and LTE transmission mode 3 may be appliedto V2X communication.

For example, FIG. 10B illustrates a UE operation related to LTEtransmission mode 2 or LTE transmission mode 4. Alternatively, forexample, FIG. 10(b) illustrates a UE operation related to NR resourceallocation mode 2.

Referring to FIG. 10A, in LTE transmission mode 1, LTE transmission mode3, or NR resource allocation mode 1, a BS may schedule SL resources tobe used for SL transmission of a UE. For example, the BS may performresource scheduling for UE 1 through a PDCCH (more specifically, DLcontrol information (DCI)), and UE 1 may perform V2X or SL communicationwith UE 2 according to the resource scheduling. For example, UE 1 maytransmit sidelink control information (SCI) to UE 2 on a PSCCH, and thentransmit data based on the SCI to UE 2 on a PSSCH.

For example, in NR resource allocation mode 1, a UE may be provided withor allocated resources for one or more SL transmissions of one transportblock (TB) by a dynamic grant from the BS. For example, the BS mayprovide the UE with resources for transmission of a PSCCH and/or a PSSCHby the dynamic grant. For example, a transmitting UE may report an SLhybrid automatic repeat request (SL HARQ) feedback received from areceiving UE to the BS. In this case, PUCCH resources and a timing forreporting the SL HARQ feedback to the BS may be determined based on anindication in a PDCCH, by which the BS allocates resources for SLtransmission.

For example, the DCI may indicate a slot offset between the DCIreception and a first SL transmission scheduled by the DCI. For example,a minimum gap between the DCI that schedules the SL transmissionresources and the resources of the first scheduled SL transmission maynot be smaller than a processing time of the UE.

For example, in NR resource allocation mode 1, the UE may beperiodically provided with or allocated a resource set for a pluralityof SL transmissions through a configured grant from the BS. For example,the grant to be configured may include configured grant type 1 orconfigured grant type 2. For example, the UE may determine a TB to betransmitted in each occasion indicated by a given configured grant.

For example, the BS may allocate SL resources to the UE in the samecarrier or different carriers.

For example, an NR gNB may control LTE-based SL communication. Forexample, the NR gNB may transmit NR DCI to the UE to schedule LTE SLresources. In this case, for example, a new RNTI may be defined toscramble the NR DCI. For example, the UE may include an NR SL module andan LTE SL module.

For example, after the UE including the NR SL module and the LTE SLmodule receives NR SL DCI from the gNB, the NR SL module may convert theNR SL DCI into LTE DCI type 5A, and transmit LTE DCI type 5A to the LTESL module every Xms. For example, after the LTE SL module receives LTEDCI format 5A from the NR SL module, the LTE SL module may activateand/or release a first LTE subframe after Z ms. For example, X may bedynamically indicated by a field of the DCI. For example, a minimumvalue of X may be different according to a UE capability. For example,the UE may report a single value according to its UE capability. Forexample, X may be positive.

Referring to FIG. 10B, in LTE transmission mode 2, LTE transmission mode4, or NR resource allocation mode 2, the UE may determine SLtransmission resources from among SL resources preconfigured orconfigured by the BS/network. For example, the preconfigured orconfigured SL resources may be a resource pool. For example, the UE mayautonomously select or schedule SL transmission resources. For example,the UE may select resources in a configured resource pool on its own andperform SL communication in the selected resources. For example, the UEmay select resources within a selection window on its own by a sensingand resource (re)selection procedure. For example, the sensing may beperformed on a subchannel basis. UE 1, which has autonomously selectedresources in a resource pool, may transmit SCI to UE 2 on a PSCCH andthen transmit data based on the SCI to UE 2 on a PSSCH.

For example, a UE may help another UE with SL resource selection. Forexample, in NR resource allocation mode 2, the UE may be configured witha grant configured for SL transmission. For example, in NR resourceallocation mode 2, the UE may schedule SL transmission for another UE.For example, in NR resource allocation mode 2, the UE may reserve SLresources for blind retransmission.

For example, in NR resource allocation mode 2, UE 1 may indicate thepriority of SL transmission to UE 2 by SCI. For example, UE 2 may decodethe SCI and perform sensing and/or resource (re)selection based on thepriority. For example, the resource (re)selection procedure may includeidentifying candidate resources in a resource selection window by UE 2and selecting resources for (re)transmission from among the identifiedcandidate resources by UE 2. For example, the resource selection windowmay be a time interval during which the UE selects resources for SLtransmission. For example, after UE 2 triggers resource (re)selection,the resource selection window may start at T1≥0, and may be limited bythe remaining packet delay budget of UE 2. For example, when specificresources are indicated by the SCI received from UE 1 by the second UEand an L1 SL reference signal received power (RSRP) measurement of thespecific resources exceeds an SL RSRP threshold in the step ofidentifying candidate resources in the resource selection window by UE2, UE 2 may not determine the specific resources as candidate resources.For example, the SL RSRP threshold may be determined based on thepriority of SL transmission indicated by the SCI received from UE 1 byUE 2 and the priority of SL transmission in the resources selected by UE2.

For example, the L1 SL RSRP may be measured based on an SL demodulationreference signal (DMRS). For example, one or more PSSCH DMRS patternsmay be configured or preconfigured in the time domain for each resourcepool. For example, PDSCH DMRS configuration type 1 and/or type 2 may beidentical or similar to a PSSCH DMRS pattern in the frequency domain.For example, an accurate DMRS pattern may be indicated by the SCI. Forexample, in NR resource allocation mode 2, the transmitting UE mayselect a specific DMRS pattern from among DMRS patterns configured orpreconfigured for the resource pool.

For example, in NR resource allocation mode 2, the transmitting UE mayperform initial transmission of a TB without reservation based on thesensing and resource (re)selection procedure. For example, thetransmitting UE may reserve SL resources for initial transmission of asecond TB using SCI associated with a first TB based on the sensing andresource (re)selection procedure.

For example, in NR resource allocation mode 2, the UE may reserveresources for feedback-based PSSCH retransmission through signalingrelated to a previous transmission of the same TB. For example, themaximum number of SL resources reserved for one transmission, includinga current transmission, may be 2, 3 or 4. For example, the maximumnumber of SL resources may be the same regardless of whether HARQfeedback is enabled. For example, the maximum number of HARQ(re)transmissions for one TB may be limited by a configuration orpreconfiguration. For example, the maximum number of HARQ(re)transmissions may be up to 32. For example, if there is noconfiguration or preconfiguration, the maximum number of HARQ(re)transmissions may not be specified. For example, the configurationor preconfiguration may be for the transmitting UE. For example, in NRresource allocation mode 2, HARQ feedback for releasing resources whichare not used by the UE may be supported.

For example, in NR resource allocation mode 2, the UE may indicate oneor more subchannels and/or slots used by the UE to another UE by SCI.For example, the UE may indicate one or more subchannels and/or slotsreserved for PSSCH (re)transmission by the UE to another UE by SCI. Forexample, a minimum allocation unit of SL resources may be a slot. Forexample, the size of a subchannel may be configured or preconfigured forthe UE.

SCI will be described below.

While control information transmitted from a BS to a UE on a PDCCH isreferred to as DCI, control information transmitted from one UE toanother UE on a PSCCH may be referred to as SCI. For example, the UE mayknow the starting symbol of the PSCCH and/or the number of symbols inthe PSCCH before decoding the PSCCH. For example, the SCI may include SLscheduling information. For example, the UE may transmit at least oneSCI to another UE to schedule the PSSCH. For example, one or more SCIformats may be defined.

For example, the transmitting UE may transmit the SCI to the receivingUE on the PSCCH. The receiving UE may decode one SCI to receive thePSSCH from the transmitting UE.

For example, the transmitting UE may transmit two consecutive SCIs(e.g., 2-stage SCI) on the PSCCH and/or PSSCH to the receiving UE. Thereceiving UE may decode the two consecutive SCIs (e.g., 2-stage SCI) toreceive the PSSCH from the transmitting UE. For example, when SCIconfiguration fields are divided into two groups in consideration of a(relatively) large SCI payload size, SCI including a first SCIconfiguration field group is referred to as first SCI. SCI including asecond SCI configuration field group may be referred to as second SCI.For example, the transmitting UE may transmit the first SCI to thereceiving UE on the PSCCH. For example, the transmitting UE may transmitthe second SCI to the receiving UE on the PSCCH and/or PSSCH. Forexample, the second SCI may be transmitted to the receiving UE on an(independent) PSCCH or on a PSSCH in which the second SCI is piggybackedto data. For example, the two consecutive SCIs may be applied todifferent transmissions (e.g., unicast, broadcast, or groupcast).

For example, the transmitting UE may transmit all or part of thefollowing information to the receiving UE by SCI. For example, thetransmitting UE may transmit all or part of the following information tothe receiving UE by first SCI and/or second SCI.

-   -   PSSCH-related and/or PSCCH-related resource allocation        information, for example, the positions/number of time/frequency        resources, resource reservation information (e.g. a        periodicity), and/or    -   an SL channel state information (CSI) report request indicator        or SL (L1) RSRP (and/or SL (L1) reference signal received        quality (RSRQ) and/or SL (L1) received signal strength indicator        (RSSI)) report request indicator, and/or    -   an SL CSI transmission indicator (on PSSCH) (or SL (L1) RSRP        (and/or SL (L1) RSRQ and/or SL (L1) RSSI) information        transmission indicator), and/or    -   MCS information, and/or    -   transmission power information, and/or    -   L1 destination ID information and/or L1 source ID information,        and/or    -   SL HARQ process ID information, and/or    -   new data indicator (NDI) information, and/or    -   redundancy version (RV) information, and/or    -   QoS information (related to transmission traffic/packet), for        example, priority information, and/or    -   an SL CSI-RS transmission indicator or information about the        number of SL CSI-RS antenna ports (to be transmitted);    -   location information about a transmitting UE or location (or        distance area) information about a target receiving UE        (requested to transmit an SL HARQ feedback), and/or    -   RS (e.g., DMRS or the like) information related to decoding        and/or channel estimation of data transmitted on a PSSCH, for        example, information related to a pattern of (time-frequency)        mapping resources of the DMRS, rank information, and antenna        port index information.

For example, the first SCI may include information related to channelsensing. For example, the receiving UE may decode the second SCI usingthe PSSCH DMRS. A polar code used for the PDCCH may be applied to thesecond SCI. For example, the payload size of the first SCI may be equalfor unicast, groupcast and broadcast in a resource pool. After decodingthe first SCI, the receiving UE does not need to perform blind decodingon the second SCI. For example, the first SCI may include schedulinginformation about the second SCI.

In various embodiments of the present disclosure, since the transmittingUE may transmit at least one of the SCI, the first SCI, or the secondSCI to the receiving UE on the PSCCH, the PSCCH may be replaced with atleast one of the SCI, the first SCI, or the second SC. Additionally oralternatively, for example, the SCI may be replaced with at least one ofthe PSCCH, the first SCI, or the second SCI. Additionally oralternatively, for example, since the transmitting UE may transmit thesecond SCI to the receiving UE on the PSSCH, the PSSCH may be replacedwith the second SCI.

In NR V2X, although a UE has multiple different application identifiers(ALIDs), the UE may have the same Layer 2 (L2) ID for different ALIDs.As illustrated in FIG. 11 , for example, PC5 unicast link A and PC5unicast link B between UE 1 and UE 2 may have different ALIDs but thesame pair of a source L2 ID and a destination L2 ID. That is, PC5unicast link A and PC5 unicast link B may have the same source L2 ID, Wand the same destination L2 ID, X in the example of FIG. 11 .

In this case, upon occurrence of sidelink radio link failure (SL RLF)for PC5 unicast link A, a UE (e.g., Tx UE or Rx UE) reports informationabout the SL RLF to a higher layer (V2X layer) and a BS. For example,the information about the SL RLF may be information notifying orindicating that RLF has occurred to the PC5 unicast link or PC5 RRCconnection. For example, the information about the SL RLF may includethe destination L2 ID. Alternatively, for example, the information aboutthe SL RLF may include both the source L2 ID and the destination L2 ID.In various embodiments of the present disclosure, information about SLRLF may be referred to as an SL RLF indication or an RLF indication. Invarious embodiments of the present disclosure, SL RLF may be referred toas PC5 RLF or RLF.

However, when the UE has established a plurality of PC5 unicast links ora plurality of PC5 RRC connections as in the example of FIG. 11 , thePC5 unicast links may have the same source L2 ID and/or the samedestination L2 ID. Therefore, the higher layer (V2X layer) of the UE orthe BS may not identify the PC5 unicast link to which the SL RLF hasoccurred among the plurality of PC5 unicast links, although the higherlayer or the BS has received a report of the SL RLF indication. Forexample, even though the higher layer (e.g., V2X layer) of the UE or theBS has received information about SL RLF including an L2 ID, W and/or anL2 ID, Z, the higher layer (e.g., V2X layer) of the UE or the BS may notidentify the PC5 unicast link to which the SL RLF has occurred betweenPC5 unicast link A and PC5 unicast link B.

Therefore, upon occurrence of SL RLF to a PC5 unicast link, the AS layerof the UE should transmit, to the higher layer (e.g., V2X layer) of theUE, a PC5 unicast link ID of the PC5 unicast link, which enables the PC5unicast link to be uniquely identified by a source L2 ID and/ordestination L2 ID. For example, the AS layer of the UE should transmitL2 link D, L2 link E, and L2 link F to the higher layer (e.g., V2Xlayer) of the UE in the example of FIG. 11 . Alternatively, uponoccurrence of SL RLF to a PC5 unicast link, the AS layer of the UEshould transmit, to the BS, a PC5 unicast link ID of the PC5 unicastlink, which enables the PC5 unicast link to be uniquely identified by asource L2 ID and/or destination L2 ID. For example, the AS layer of theUE should transmit L2 link D, L2 link E, and L2 link F to the BS in theexample of FIG. 11 . For example, the PC5 unicast link IDs may be IDsthat identify the PC5 unicast links, which have been received from theV2X layer of the UE by the AS layer of the UE.

Accordingly, a method and apparatus for operating a UE, upon occurrenceof SL RLF to a PC5 unicast link among a plurality of PC5 unicast linksaccording to various embodiment of the present disclosure are proposedbelow. The various embodiments of the present disclosure may beimplemented in combination with a transmission and reception operationin a BW and/or a synchronization operation of a UE. One or more of thefollowing embodiments may be implemented in combination.

According to an embodiment, a first UE (UE 1) may establish two or morePC5 RRC connections with a second UE (UE 2) (S1201 in FIG. 12 ). UE 1may then release a PC5 RRC connection for which SL RLF has been declaredamong the two or more PC5 RRC connections (S1202 in FIG. 12 ).

There may be a PC5 unicast link associated with the PC5 RRC connection,and the PC5 unicast link for which the SL RLF has been declared and thePC5 RRC connection has been released may be indicated by a PC5 linkIdentifier. PC5 RRC connections may be mapped to PC5 unicast links in aone-to-one correspondence.

The PC5 link Identifier may be delivered from the AS layer of UE 1 tothe V2X layer of UE 1. The V2X layer releases the PC5 unicast linkindicated by the PC5 link Identifier. The PC5 unicast link is related tothe PC5 RRC connection which has been released due to the SL RLF. Thatis, the AS layer of UE 1 indicates to the V2X layer of UE 1 that the PC5RRC connection has been released based on the SL RLF. In other words,once SL RLF is declared for a PC5 unicast link, the AS layer of the UEmay release a PC5 RRC connection to which the SL RLF has occurred. TheAS layer of the UE may release the PC5 RRC connection to which the SLRLF has occurred and transmit information (or an indication) about thePC5 unicast link associated with the released PC5 RRC connection to thehigher layer (V2X layer) of the UE. Upon receipt of a report of theindication including the information about the PC5 unicast linkassociated with the PC5 RRC connection which has been released due tothe SL RLF from the AS layer of the UE, the higher layer of the UE mayrelease a PC5-S connection associated with the PC5 link Identifier. Thatis, the higher layer may release the PC5 unicast link associated withthe PC5 RRC connection.

The information about the PC5 unicast link may be the afore-describedPC5 link Identifier. In another example, the information about the PC5unicast link may be an ID that identifies the PC5 unicast link uniquely.For example, the information about the PC5 unicast link may include atleast one of the PC5 unicast link ID, a source L2 ID associated with thePC5 unicast link ID, a destination L2 ID associated with the PC5 unicastlink ID, an ALID of a source UE associated with the PC5 unicast link ID,and/or an ALID of a destination UE associated with the PC5 unicast linkID. Alternatively, the information about the PC5 unicast link mayinclude all of the above information.

In summary, when the V2X layer receives a notification indicating that aPC5 RRC connection of any PC5 unicast link has been released due to SLRLF from the AS layer, the V2X layer locally releases the PC5 unicastlink. The AS layer uses a PC5 link Identifier to indicate the PC5unicast link for which the PC5 RRC connection has been released. (Whenthe V2X layer is informed by the AS layer that any PC5 unicast link'sPC5-RRC connection was released, due to RLF, the V2X layer locallyreleases the PC5 unicast link. The AS layer uses PC5 Link Identifier toindicate the PC5 unicast link whose PC5-RRC connection was released.)

According to the above configuration, in the case where an SL UE hasestablished two or more PC5 unicast links and two or more PC5 RRCconnections with another UE, when a PC5 RRC connection is released dueto SL RLF declaration, a PC5 unicast link corresponding to the releasedPC5 RRC connection among the two or more PC5 unicast links may beindicated explicitly. Accordingly, the problem that the higher layer ofthe UE or the BS has no way to identify a PC5 unicast link to which SLRLF has occurred as described before with reference to FIG. 11 may besolved. More specifically, upon occurrence of SL RLF to a PC5 unicastlink, the UE may immediately release a PC5 RRC connection to which theSL RLF has occurred, and forward or transmit a PC5 unicast link IDidentifying the PC5 unicast link along with a “PC5 RRC connectionrelease” indication to the higher layer (e.g., V2X layer) of the UE orthe BS. Therefore, even though the UE maintains a plurality of PC5unicast links, the B S or the higher layer of the UE may identify a PC5unicast link to which SL RLF has occurred. Accordingly, the UE maynormally release the PC5 unicast link to which PC5 RLF (or SL RLF) hasoccurred.

Further, according to various embodiments of the present disclosure,when a PC5 RRC connection has been released, the UE may forward ortransmit information about a PC5 unicast link associated with the PC5RRC connection released by the UE to the higher layer (e.g., V2X layer)of the or the BS. Therefore, even though the UE maintains a plurality ofPC5 unicast links, the BS or the higher layer of the UE may identify aPC5 unicast link for which a PC5 RRC connection has been released.Accordingly, the UE may normally release the PC5 unicast link for whichthe PC5 RRC connection has been released.

FIG. 13 is a diagram illustrating a signal flow for a method ofreleasing a PC5 RRC connection and reporting the release of the PC5 RRCconnection to a higher layer by a UE and thus releasing a PC5 unicastlink by the higher layer according to an embodiment of the presentdisclosure.

Referring to FIG. 13 , a first UE (UE 1) and a second UE (UE 2) may setup/establish a plurality of PC5 unicast links in operation S1301. PC5unicast link “A” and PC5 unicast link “B” may have the same source L2ID, X and the same destination L2 ID, Y. UE 1 may be a source UE and UE2 may be a destination UE.

In operation S1302, a higher layer of UE 1 may transmit an IDidentifying PC5 unicast link “A” uniquely, that is, PC5 unicast link ID“AA” to the AS layer of UE 1. Further, the higher layer of UE 1 maytransmit an ID identifying PC5 unicast link “B” uniquely, that is, PC5unicast link ID “BB” to the AS layer of UE 1. For example, the higherlayer may be a V2X layer. According to an embodiment of the presentdisclosure, even though a plurality of PC5 unicast links have the samesource L2 ID and/or the same destination L2 ID, the AS layer of the UEmay distinguish the PC5 unicast links having the same source L2 IDand/or the same destination L2 ID from each other based on PC5 unicastlink IDs received from the higher layer of the UE.

Upon occurrence of RLF to PC5 unicast link “A”, the AS layer of UE 1 mayrelease a PC5 RRC connection of PC5 unicast link “A” to which the RLFhas occurred in operation S1303. The AS layer of UE 1 may also transmita “PC5 RRC connection release” indication to the V2X layer. For example,the “PC5 RRC connection release” indication may be anindication/information by which the AS layer of the UE indicates therelease of the PC5 RRC connection to the higher layer of the UE. Forexample, the “PC5 RRC connection release” indication may includeinformation about a PC5 unicast link ID identifying a PC5 unicast linkassociated with the PC5 RRC connection which has been released due tothe RLF.

In operation S1304, the higher layer of UE 1 may check the “PC5 RRCconnection release” indication received from the AS layer of UE 1. Thehigher layer of UE 1 may release a PC5-S connection mapped to the PC5unicast link ID. That is, the higher layer of UE 1 may release the PC5unicast link mapped to the PC5 unicast link ID.

UE 1 may transmit, to the BS, information about the PC5 unicast link forwhich the SL RLF has been declared and thus the PC5 RRC connection hasbeen released. A related embodiment will be described below.

Once a UE (e.g., Tx UE or Rx UE) declares RLF for a PC5 unicast link,the UE may immediately releases a PC5 RRC connection to which the SL RLFhas occurred and transmit a “PC5 RRC connection release (or PC5 RLFindication)” message including information about the PC5 unicast linkassociated with the PC5 RRC connection released due to the PC5 RLF tothe BS. For example, the information about the PC5 unicast link may bean ID identifying the PC5 unicast link uniquely. For example, theinformation about the PC5 unicast link may include at least one of thePC5 unicast link ID, a source L2 ID associated with the PC5 unicast linkID, a destination L2 ID associated with the PC5 unicast link ID, an ALIDof a source UE associated with the PC5 unicast link ID, and/or an ALIDof a destination UE associated with the PC5 unicast link ID.Alternatively, the information about the PC5 unicast link may includeall of the above information. For example, the “PC5 RRC connectionrelease” message may be transmitted in an RRC message. For example, theRRC message may be a Sidelink UE Information message or a new RRCmessage.

Upon receipt of the “PC5 RRC connection release” message including theinformation about the PC5 unicast link from the UE, the BS may releaseall of radio resources associated with the PC5 unicast link. Forexample, the radio resources may include mode 1 resources and/or mode 2resources. For example, the mode 1 resources may be resources that theBS has allocated to the UE, for SL communication, and the mode 2resources may be resources that the UE has allocated or selected for theSL communication.

FIG. 14 is a diagram illustrating a method of releasing a PC5 RRCconnection and reporting the release of the PC5 RRC connection to a BSby a UE and releasing radio resources from the UE by the BS according toan embodiment of the present disclosure.

Referring to FIG. 14 , UE 1 and UE 2 may set up/establish a plurality ofPC5 unicast links in operation S1401. PC5 unicast link “A” and PC5unicast link “B” may have the same source L2 ID, X and the samedestination L2 ID, Y. UE 1 may be a source UE and UE 2 may be adestination UE.

In operation S1402, a higher layer of UE 1 may transmit an IDidentifying PC5 unicast link “A” uniquely, that is, PC5 unicast link ID“AA” to the AS layer of UE 1. Further, the higher layer of UE 1 maytransmit an ID identifying PC5 unicast link “B” uniquely, that is, PC5unicast link ID “BB” to the AS layer of UE 1. For example, the higherlayer may be a V2X layer. According to an embodiment of the presentdisclosure, even though a plurality of PC5 unicast links have the samesource L2 ID and/or the same destination L2 ID, the AS layer of the UEmay distinguish the PC5 unicast links having the same source L2 IDand/or the same destination L2 ID from each other based on PC5 unicastlink IDs received from the higher layer of the UE.

Upon occurrence of RLF to PC5 unicast link “A”, UE 1 may transmit a “PC5RRC connection release indication” message to the BS in operation S1403.For example, the PC5 RRC connection release indication may be anindication/information by which UE 1 indicates the release of a PC5 RRCconnection to the BS. For example, the “PC5 RRC connection releaseindication” message may include information about a PC5 unicast link IDidentifying the PC5 unicast link associated with the PC5 RRC connectionwhich has been released due to the SL RLF. In the embodiment of FIG. 14, for example, the “PC5 RRC connection release indication” message mayinclude information about a PC5 unicast link ID identifying PC5 unicastlink “A” associated with the PC5 RRC connection released due to the SLRLF. For example, the “PC5 RRC connection release indication” messagemay include at least one of the PC5 unicast link ID associated with thePC5 RRC connection released due to the SL RLF, a source L2 ID associatedwith the PC5 unicast link ID, a destination L2 ID associated with thePC5 unicast link ID, an ALID of a source UE associated with the PC5unicast link ID, and/or an ALID of a destination UE associated with thePC5 unicast link ID. For example, the “PC5 RRC connection releaseindication” message may include all of the above information.

In operation S1404, the BS may retrieve or release all of radioresources allocated to PC5 unicast link “A” (e.g., mode 1 resourcesand/or mode 2 resources).

Now, a description will be given of release of a PC5 RRC connection thatoccurs for a reason other than SL RLF. When a PC5 RRC connection isreleased for a reason other than SL RLF among the two or more PC5 RRCconnections, UE 1 may transmit information about a PC5 unicast linkassociated with the PC5 RRC connection to the BS. When the AS layer ofthe UE releases a PC5 RRC connection for a PC5 unicast link for a reasonother than PC5 RLF, the AS layer of the UE may transmit information (oran indication) about the PC5 unicast link associated with the releasedPC5 RRC connection to the higher layer of the UE.

The reason other than SL (or PC5) RLF, for example, a cause other thanPC5 RLF, which leads to the UE's release of a PC5 RRC connection for aPC5 unicast link may be any of the following causes:

-   -   PC5 RRC resume failure;    -   PC5 RRC connection failure;    -   PC5 RRC suspension;    -   load balancing required for PC5 interface;    -   mismatch between UE capabilities of UEs (e.g., a Tx UE and a        peer Rx UE); and    -   AS layer configuration failure between UEs (e.g., a Tx UE and a        peer Rx UE).

For example, the higher layer may be the V2X layer in the proposal. Forexample, the information about the PC5 unicast link may be an ID thatuniquely identifies the PC5 unicast link. For example, the informationabout the PC5 unicast link may include at least one of a PC5 unicastlink ID, a source L2 ID associated with the PC5 unicast link ID, adestination L2 ID associated with the PC5 unicast link ID, an ALID of asource UE associated with the PC5 unicast link ID, and/or an ALID of adestination UE associated with the PC5 unicast link ID. For example, theinformation about the PC5 unicast link may include all of the aboveinformation.

For example, upon receipt of a report of an indication including theinformation about the PC5 unicast link associated with the PC5 RRCconnection from the AS layer of the UE, the higher layer of the UE mayrelease a PC5-S connection associated with the PC5 unicast link ID. Thatis, the higher layer may release the PC5 unicast link associated withthe PC5 RRC connection.

In relation to the above description, when the AS layer of the UEreleases a PC5 RRC connection for a PC5 unicast link for a reason otherthan PC5 RLF, the AS layer of the UE may transmit a “PC5 RRC connectionrelease” message including information about the PC5 unicast linkassociated with the released PC5 RRC connection to the BS. The reasonother than PC5 RLF may be any of PC5 RRC resume failure, PC5 RRCconnection failure, PC5 RRC suspension, load balancing required for PC5interface, mismatch between the UE capabilities of UEs (e.g., a Tx UEand a peer Rx UE), and AS layer configuration failure between UEs (e.g.,a Tx UE and a peer Rx UE).

Further, the information about the PC5 unicast link may be, for example,an ID identifying the PC5 unicast link uniquely. For example, theinformation about the PC5 unicast link may include at least one of a PC5unicast link ID, a source L2 ID associated with the PC5 unicast link ID,a destination L2 ID associated with the PC5 unicast link ID, an ALID ofa source UE associated with the PC5 unicast link ID, and/or an ALID of adestination UE associated with the PC5 unicast link ID. For example, theinformation about the PC5 unicast link may include all of the aboveinformation.

For example, the “PC5 RRC connection release” message may be transmittedin an RRC message. For example, the RRC message may be a Sidelink UEInformation message or a new RRC message.

Upon receipt of the “PC5 RRC connection release” message including theinformation about the PC5 unicast link from the UE, the BS may releaseall of radio resources associated with the PC5 unicast link. Forexample, the radio resources may include mode 1 resources and/or mode 2resources. For example, the mode 1 resources may be resources that theBS has allocated to the UE, for SL communication, and the mode 2resources may be resources that the UE has allocated or selected for theSL communication.

When the AS layer of the UE determines to release a PC5 RRC connectionfor a PC5 unicast link for a reason other than PC5 RLF, the AS layer ofthe UE may transmit information (or an indication) about the PC5 unicastlink associated with the PC5 RRC connection determined to be released tothe higher layer of the UE. The reason other than PC5 RLF has beendescribed before. Further, the higher layer may be the V2X layer in theproposal. For example, the information about the PC5 unicast link mayinclude at least one of a PC5 unicast link ID, a source L2 ID associatedwith the PC5 unicast link ID, a destination L2 ID associated with thePC5 unicast link ID, an ALID of a source UE associated with the PC5unicast link ID, and/or an ALID of a destination UE associated with thePC5 unicast link ID. For example, the information about the PC5 unicastlink may include all of the above information.

For example, upon receipt of a report of an indication including theinformation about the PC5 unicast link associated with the PC5 RRCconnection determined to be released by the AS layer of the UE from theAS layer of the UE, the higher layer of the UE may release a PC5-Sconnection associated with the PC5 unicast link ID. That is, the higherlayer may release the PC5 unicast link or connection associated with thePC5 RRC connection. After releasing the PC5 unicast link, the higherlayer of the UE may indicate to the AS layer of the UE to release thePC5 RRC connection associated with the PC5 unicast link. When indicatingto the AS layer of the UE to release the PC5 RRC connection, the higherlayer of the UE may transmit information about the PC5 unicast link tothe AS layer of the UE. Upon receipt of the indication to release thePC5 RRC connection from the higher layer of the UE, the AS layer of theUE may release the PC5 RRC connection associated with the PC5 unicastlink.

In another example, when the AS layer of the UE determines to release aPC5 RRC connection for a PC5 unicast link for a reason other than PC5RLF, the AS layer of the UE may transmit a “PC5 RRC connection releaserequest” message including information about the PC5 unicast linkassociated with the PC5 RRC connection determined to be released to theBS. The reason other than PC5 RLF has been described before.

Further, the information about the PC5 unicast link may be, for example,an ID identifying the PC5 unicast link uniquely. For example, theinformation about the PC5 unicast link may include at least one of a PC5unicast link ID, a source L2 ID associated with the PC5 unicast link ID,a destination L2 ID associated with the PC5 unicast link ID, an ALID ofa source UE associated with the PC5 unicast link ID, and/or an ALID of adestination UE associated with the PC5 unicast link ID. For example, theinformation about the PC5 unicast link may include all of the aboveinformation. For example, the “PC5 RRC connection release request”message may be transmitted in an RRC message. For example, the RRCmessage may be a Sidelink UE Information message or a new RRC message.

Upon receipt of the “PC5 RRC connection release request” messageincluding the information about the PC5 unicast link from the UE, the BSmay determine to release the PC5 RRC connection of the UE. For example,when determining to release the PC5 RRC connection of the UE, the BS maytransmit a “PC5 RRC connection release confirm” message to the UE. The“PC5 RRC connection release confirm” message may include informationabout the PC5 unicast link associated with the PC5 RRC connectiondetermined to be released by the BS. For example, after transmitting the“PC5 RRC connection release confirm” message, the BS may release all ofradio resources associated with the PC5 unicast link. For example, theradio resources may include mode 1 resources and/or mode 2 resources.For example, the mode 1 resources may be resources that the BS hasallocated to the UE, for SL communication, and the mode 2 resources maybe resources that the UE has allocated or selected for the SLcommunication.

In another embodiment, when the higher layer of the UE determines not toconfigure any more NR SL transmission configuration or any more NR SLreception configuration, the AS layer of the UE may transmit, to the BS,a Sidelink UE Information message or RRC message including informationabout the PC5 unicast link determined by the higher layer, so that theAS layer of the UE may not perform a transmission and a receptionrelated to NR SL. For example, the information about the PC5 unicastlink may be an ID that uniquely identifies the PC5 unicast link. Forexample, the information about the PC5 unicast link may include at leastone of a PC5 unicast link ID, a source L2 ID associated with the PC5unicast link ID, a destination L2 ID associated with the PC5 unicastlink ID, an ALID of a source UE associated with the PC5 unicast link ID,and/or an ALID of a destination UE associated with the PC5 unicast linkID. For example, the information about the PC5 unicast link may includeall of the above information.

For example, upon receipt of the Sidelink UE Information messageincluding the information about the PC5 unicast link from the UE, the BSmay release all AS contexts related to the PC5 unicast link identifiedby the PC5 unicast link ID included in the Sidelink UE Informationmessage. Further the BS may release all of radio resources associatedwith the PC5 unicast link. For example, the radio resources may includemode 1 resources and/or mode 2 resources. For example, the mode 1resources may be resources that the BS has allocated to the UE, for SLcommunication, and the mode 2 resources may be resources that the UE hasallocated or selected for the SL communication.

FIG. 15 illustrates a method of, when a UE determines not to conduct SLcommunication any longer, transmitting, to a BS, a Sidelink UEInformation message including information about a PC5 unicast link onwhich the UE will not transmit/receive SL data any longer by the UE, sothat the BS releases radio resources from the UE.

Examples of Communication Systems Applicable to the Present Disclosure

The various descriptions, functions, procedures, proposals, methods,and/or operational flowcharts of the present disclosure described inthis document may be applied to, without being limited to, a variety offields requiring wireless communication/connection (e.g., 5G) betweendevices.

Hereinafter, a description will be given in more detail with referenceto the drawings. In the following drawings/description, the samereference symbols may denote the same or corresponding hardware blocks,software blocks, or functional blocks unless described otherwise.

FIG. 16 illustrates a communication system 1 applied to the presentdisclosure.

Referring to FIG. 16 , a communication system 1 applied to the presentdisclosure includes wireless devices, BSs, and a network. Herein, thewireless devices represent devices performing communication using RAT(e.g., 5G NR or LTE) and may be referred to as communication/radio/5Gdevices. The wireless devices may include, without being limited to, arobot 100 a, vehicles 100 b-1 and 100 b-2, an extended reality (XR)device 100 c, a hand-held device 100 d, a home appliance 100 e, anInternet of things (IoT) device 100 f, and an artificial intelligence(AI) device/server 400. For example, the vehicles may include a vehiclehaving a wireless communication function, an autonomous driving vehicle,and a vehicle capable of performing communication between vehicles.Herein, the vehicles may include an unmanned aerial vehicle (UAV) (e.g.,a drone). The XR device may include an augmented reality (AR)/virtualreality (VR)/mixed reality (MR) device and may be implemented in theform of a head-mounted device (HMD), a head-up display (HUD) mounted ina vehicle, a television, a smartphone, a computer, a wearable device, ahome appliance device, a digital signage, a vehicle, a robot, etc. Thehand-held device may include a smartphone, a smartpad, a wearable device(e.g., a smartwatch or a smartglasses), and a computer (e.g., anotebook). The home appliance may include a TV, a refrigerator, and awashing machine. The IoT device may include a sensor and a smartmeter.For example, the BSs and the network may be implemented as wirelessdevices and a specific wireless device 200 a may operate as a BS/networknode with respect to other wireless devices.

The wireless devices 100 a to 100 f may be connected to the network 300via the BSs 200. An AI technology may be applied to the wireless devices100 a to 100 f and the wireless devices 100 a to 100 f may be connectedto the AI server 400 via the network 300. The network 300 may beconfigured using a 3G network, a 4G (e.g., LTE) network, or a 5G (e.g.,NR) network. Although the wireless devices 100 a to 100 f maycommunicate with each other through the BSs 200/network 300, thewireless devices 100 a to 100 f may perform direct communication (e.g.,sidelink communication) with each other without passing through theBSs/network. For example, the vehicles 100 b-1 and 100 b-2 may performdirect communication (e.g. V2V/V2X communication). The IoT device (e.g.,a sensor) may perform direct communication with other IoT devices (e.g.,sensors) or other wireless devices 100 a to 100 f.

Wireless communication/connections 150 a, 150 b, or 150 c may beestablished between the wireless devices 100 a to 100 f/BS 200, or BS200/BS 200. Herein, the wireless communication/connections may beestablished through various RATs (e.g., 5G NR) such as UL/DLcommunication 150 a, sidelink communication 150 b (or, D2Dcommunication), or inter BS communication (e.g. relay, integrated accessbackhaul (IAB)). The wireless devices and the BSs/the wireless devicesmay transmit/receive radio signals to/from each other through thewireless communication/connections 150 a and 150 b. For example, thewireless communication/connections 150 a and 150 b may transmit/receivesignals through various physical channels. To this end, at least a partof various configuration information configuring processes, varioussignal processing processes (e.g., channel encoding/decoding,modulation/demodulation, and resource mapping/demapping), and resourceallocating processes, for transmitting/receiving radio signals, may beperformed based on the various proposals of the present disclosure.

Examples of Wireless Devices Applicable to the Present Disclosure

FIG. 17 illustrates wireless devices applicable to the presentdisclosure.

Referring to FIG. 17 , a first wireless device 100 and a second wirelessdevice 200 may transmit radio signals through a variety of RATs (e.g.,LTE and NR). Herein, {the first wireless device 100 and the secondwireless device 200} may correspond to {the wireless device 100 x andthe BS 200} and/or {the wireless device 100 x and the wireless device100 x} of FIG. 16 .

The first wireless device 100 may include one or more processors 102 andone or more memories 104 and additionally further include one or moretransceivers 106 and/or one or more antennas 108. The processor(s) 102may control the memory(s) 104 and/or the transceiver(s) 106 and may beconfigured to implement the descriptions, functions, procedures,proposals, methods, and/or operational flowcharts disclosed in thisdocument. For example, the processor(s) 102 may process informationwithin the memory(s) 104 to generate first information/signals and thentransmit radio signals including the first information/signals throughthe transceiver(s) 106. The processor(s) 102 may receive radio signalsincluding second information/signals through the transceiver 106 andthen store information obtained by processing the secondinformation/signals in the memory(s) 104. The memory(s) 104 may beconnected to the processor(s) 102 and may store a variety of informationrelated to operations of the processor(s) 102. For example, thememory(s) 104 may store software code including commands for performinga part or the entirety of processes controlled by the processor(s) 102or for performing the descriptions, functions, procedures, proposals,methods, and/or operational flowcharts disclosed in this document.Herein, the processor(s) 102 and the memory(s) 104 may be a part of acommunication modem/circuit/chip designed to implement RAT (e.g., LTE orNR). The transceiver(s) 106 may be connected to the processor(s) 102 andtransmit and/or receive radio signals through one or more antennas 108.Each of the transceiver(s) 106 may include a transmitter and/or areceiver. The transceiver(s) 106 may be interchangeably used with RadioFrequency (RF) unit(s). In the present disclosure, the wireless devicemay represent a communication modem/circuit/chip.

The second wireless device 200 may include one or more processors 202and one or more memories 204 and additionally further include one ormore transceivers 206 and/or one or more antennas 208. The processor(s)202 may control the memory(s) 204 and/or the transceiver(s) 206 and maybe configured to implement the descriptions, functions, procedures,proposals, methods, and/or operational flowcharts disclosed in thisdocument. For example, the processor(s) 202 may process informationwithin the memory(s) 204 to generate third information/signals and thentransmit radio signals including the third information/signals throughthe transceiver(s) 206. The processor(s) 202 may receive radio signalsincluding fourth information/signals through the transceiver(s) 106 andthen store information obtained by processing the fourthinformation/signals in the memory(s) 204. The memory(s) 204 may beconnected to the processor(s) 202 and may store a variety of informationrelated to operations of the processor(s) 202. For example, thememory(s) 204 may store software code including commands for performinga part or the entirety of processes controlled by the processor(s) 202or for performing the descriptions, functions, procedures, proposals,methods, and/or operational flowcharts disclosed in this document.Herein, the processor(s) 202 and the memory(s) 204 may be a part of acommunication modem/circuit/chip designed to implement RAT (e.g., LTE orNR). The transceiver(s) 206 may be connected to the processor(s) 202 andtransmit and/or receive radio signals through one or more antennas 208.Each of the transceiver(s) 206 may include a transmitter and/or areceiver. The transceiver(s) 206 may be interchangeably used with RFunit(s). In the present disclosure, the wireless device may represent acommunication modem/circuit/chip.

Hereinafter, hardware elements of the wireless devices 100 and 200 willbe described more specifically. One or more protocol layers may beimplemented by, without being limited to, one or more processors 102 and202. For example, the one or more processors 102 and 202 may implementone or more layers (e.g., functional layers such as PHY, MAC, RLC, PDCP,RRC, and SDAP). The one or more processors 102 and 202 may generate oneor more Protocol Data Units (PDUs) and/or one or more service data unit(SDUs) according to the descriptions, functions, procedures, proposals,methods, and/or operational flowcharts disclosed in this document. Theone or more processors 102 and 202 may generate messages, controlinformation, data, or information according to the descriptions,functions, procedures, proposals, methods, and/or operational flowchartsdisclosed in this document. The one or more processors 102 and 202 maygenerate signals (e.g., baseband signals) including PDUs, SDUs,messages, control information, data, or information according to thedescriptions, functions, procedures, proposals, methods, and/oroperational flowcharts disclosed in this document and provide thegenerated signals to the one or more transceivers 106 and 206. The oneor more processors 102 and 202 may receive the signals (e.g., basebandsignals) from the one or more transceivers 106 and 206 and acquire thePDUs, SDUs, messages, control information, data, or informationaccording to the descriptions, functions, procedures, proposals,methods, and/or operational flowcharts disclosed in this document.

The one or more processors 102 and 202 may be referred to ascontrollers, microcontrollers, microprocessors, or microcomputers. Theone or more processors 102 and 202 may be implemented by hardware,firmware, software, or a combination thereof. As an example, one or moreapplication specific integrated circuits (ASICs), one or more digitalsignal processors (DSPs), one or more digital signal processing devices(DSPDs), one or more programmable logic devices (PLDs), or one or morefield programmable gate arrays (FPGAs) may be included in the one ormore processors 102 and 202. The descriptions, functions, procedures,proposals, methods, and/or operational flowcharts disclosed in thisdocument may be implemented using firmware or software and the firmwareor software may be configured to include the modules, procedures, orfunctions. Firmware or software configured to perform the descriptions,functions, procedures, proposals, methods, and/or operational flowchartsdisclosed in this document may be included in the one or more processors102 and 202 or stored in the one or more memories 104 and 204 so as tobe driven by the one or more processors 102 and 202. The descriptions,functions, procedures, proposals, methods, and/or operational flowchartsdisclosed in this document may be implemented using firmware or softwarein the form of code, commands, and/or a set of commands.

The one or more memories 104 and 204 may be connected to the one or moreprocessors 102 and 202 and store various types of data, signals,messages, information, programs, code, instructions, and/or commands.The one or more memories 104 and 204 may be configured by read-onlymemories (ROMs), random access memories (RAMs), electrically erasableprogrammable read-only memories (EPROMs), flash memories, hard drives,registers, cash memories, computer-readable storage media, and/orcombinations thereof. The one or more memories 104 and 204 may belocated at the interior and/or exterior of the one or more processors102 and 202. The one or more memories 104 and 204 may be connected tothe one or more processors 102 and 202 through various technologies suchas wired or wireless connection.

The one or more transceivers 106 and 206 may transmit user data, controlinformation, and/or radio signals/channels, mentioned in the methodsand/or operational flowcharts of this document, to one or more otherdevices. The one or more transceivers 106 and 206 may receive user data,control information, and/or radio signals/channels, mentioned in thedescriptions, functions, procedures, proposals, methods, and/oroperational flowcharts disclosed in this document, from one or moreother devices. For example, the one or more transceivers 106 and 206 maybe connected to the one or more processors 102 and 202 and transmit andreceive radio signals. For example, the one or more processors 102 and202 may perform control so that the one or more transceivers 106 and 206may transmit user data, control information, or radio signals to one ormore other devices. The one or more processors 102 and 202 may performcontrol so that the one or more transceivers 106 and 206 may receiveuser data, control information, or radio signals from one or more otherdevices. The one or more transceivers 106 and 206 may be connected tothe one or more antennas 108 and 208 and the one or more transceivers106 and 206 may be configured to transmit and receive user data, controlinformation, and/or radio signals/channels, mentioned in thedescriptions, functions, procedures, proposals, methods, and/oroperational flowcharts disclosed in this document, through the one ormore antennas 108 and 208. In this document, the one or more antennasmay be a plurality of physical antennas or a plurality of logicalantennas (e.g., antenna ports). The one or more transceivers 106 and 206may convert received radio signals/channels etc. from RF band signalsinto baseband signals in order to process received user data, controlinformation, radio signals/channels, etc. using the one or moreprocessors 102 and 202. The one or more transceivers 106 and 206 mayconvert the user data, control information, radio signals/channels, etc.processed using the one or more processors 102 and 202 from the baseband signals into the RF band signals. To this end, the one or moretransceivers 106 and 206 may include (analog) oscillators and/orfilters.

Examples of a Vehicle or an Autonomous Driving Vehicle Applicable to thePresent Disclosure

FIG. 18 illustrates a vehicle or an autonomous driving vehicle appliedto the present disclosure. The vehicle or autonomous driving vehicle maybe implemented by a mobile robot, a car, a train, a manned/unmannedaerial vehicle (AV), a ship, etc.

Referring to FIG. 18 , a vehicle or autonomous driving vehicle 100 mayinclude an antenna unit 108, a communication unit 110, a control unit120, a driving unit 140 a, a power supply unit 140 b, a sensor unit 140c, and an autonomous driving unit 140 d. The antenna unit 108 may beconfigured as a part of the communication unit 110.

The communication unit 110 may transmit and receive signals (e.g., dataand control signals) to and from external devices such as othervehicles, BSs (e.g., gNBs and road side units), and servers. The controlunit 120 may perform various operations by controlling elements of thevehicle or the autonomous driving vehicle 100. The control unit 120 mayinclude an ECU. The driving unit 140 a may cause the vehicle or theautonomous driving vehicle 100 to drive on a road. The driving unit 140a may include an engine, a motor, a powertrain, a wheel, a brake, asteering device, etc. The power supply unit 140 b may supply power tothe vehicle or the autonomous driving vehicle 100 and include awired/wireless charging circuit, a battery, etc. The sensor unit 140 cmay acquire a vehicle state, ambient environment information, userinformation, etc. The sensor unit 140 c may include an inertialmeasurement unit (IMU) sensor, a collision sensor, a wheel sensor, aspeed sensor, a slope sensor, a weight sensor, a heading sensor, aposition module, a vehicle forward/backward sensor, a battery sensor, afuel sensor, a tire sensor, a steering sensor, a temperature sensor, ahumidity sensor, an ultrasonic sensor, an illumination sensor, a pedalposition sensor, etc. The autonomous driving unit 140 d may implementtechnology for maintaining a lane on which a vehicle is driving,technology for automatically adjusting speed, such as adaptive cruisecontrol, technology for autonomously driving along a determined path,technology for driving by automatically setting a path if a destinationis set, and the like.

For example, the communication unit 110 may receive map data, trafficinformation data, etc. from an external server. The autonomous drivingunit 140 d may generate an autonomous driving path and a driving planfrom the obtained data. The control unit 120 may control the drivingunit 140 a such that the vehicle or the autonomous driving vehicle 100may move along the autonomous driving path according to the driving plan(e.g., speed/direction control). In the middle of autonomous driving,the communication unit 110 may aperiodically/periodically acquire recenttraffic information data from the external server and acquiresurrounding traffic information data from neighboring vehicles. In themiddle of autonomous driving, the sensor unit 140 c may obtain a vehiclestate and/or surrounding environment information. The autonomous drivingunit 140 d may update the autonomous driving path and the driving planbased on the newly obtained data/information. The communication unit 110may transfer information about a vehicle position, the autonomousdriving path, and/or the driving plan to the external server. Theexternal server may predict traffic information data using AItechnology, etc., based on the information collected from vehicles orautonomous driving vehicles and provide the predicted trafficinformation data to the vehicles or the autonomous driving vehicles.

Examples of a Vehicle and AR/VR Applicable to the Present Disclosure

FIG. 19 illustrates a vehicle applied to the present disclosure. Thevehicle may be implemented as a transport means, an aerial vehicle, aship, etc.

Referring to FIG. 19 , a vehicle 100 may include a communication unit110, a control unit 120, a memory unit 130, an I/O unit 140 a, and apositioning unit 140 b.

The communication unit 110 may transmit and receive signals (e.g., dataand control signals) to and from external devices such as other vehiclesor BSs. The control unit 120 may perform various operations bycontrolling constituent elements of the vehicle 100. The memory unit 130may store data/parameters/programs/code/commands for supporting variousfunctions of the vehicle 100. The I/O unit 140 a may output an AR/VRobject based on information within the memory unit 130. The I/O unit 140a may include an HUD. The positioning unit 140 b may acquire informationabout the position of the vehicle 100. The position information mayinclude information about an absolute position of the vehicle 100,information about the position of the vehicle 100 within a travelinglane, acceleration information, and information about the position ofthe vehicle 100 from a neighboring vehicle. The positioning unit 140 bmay include a GPS and various sensors.

As an example, the communication unit 110 of the vehicle 100 may receivemap information and traffic information from an external server andstore the received information in the memory unit 130. The positioningunit 140 b may obtain the vehicle position information through the GPSand various sensors and store the obtained information in the memoryunit 130. The control unit 120 may generate a virtual object based onthe map information, traffic information, and vehicle positioninformation and the I/O unit 140 a may display the generated virtualobject in a window in the vehicle (1410 and 1420). The control unit 120may determine whether the vehicle 100 normally drives within a travelinglane, based on the vehicle position information. If the vehicle 100abnormally exits from the traveling lane, the control unit 120 maydisplay a warning on the window in the vehicle through the I/O unit 140a. In addition, the control unit 120 may broadcast a warning messageregarding driving abnormity to neighboring vehicles through thecommunication unit 110. According to situation, the control unit 120 maytransmit the vehicle position information and the information aboutdriving/vehicle abnormality to related organizations.

Examples of an XR Device Applicable to the Present Disclosure

FIG. 20 illustrates an XR device applied to the present disclosure. TheXR device may be implemented by an HMD, an HUD mounted in a vehicle, atelevision, a smartphone, a computer, a wearable device, a homeappliance, a digital signage, a vehicle, a robot, etc.

Referring to FIG. 20 , an XR device 100 a may include a communicationunit 110, a control unit 120, a memory unit 130, an I/O unit 140 a, asensor unit 140 b, and a power supply unit 140 c.

The communication unit 110 may transmit and receive signals (e.g., mediadata and control signals) to and from external devices such as otherwireless devices, hand-held devices, or media servers. The media datamay include video, images, and sound. The control unit 120 may performvarious operations by controlling constituent elements of the XR device100 a. For example, the control unit 120 may be configured to controland/or perform procedures such as video/image acquisition, (video/image)encoding, and metadata generation and processing. The memory unit 130may store data/parameters/programs/code/commands needed to drive the XRdevice 100 a/generate XR object. The I/O unit 140 a may obtain controlinformation and data from the exterior and output the generated XRobject. The I/O unit 140 a may include a camera, a microphone, a userinput unit, a display unit, a speaker, and/or a haptic module. Thesensor unit 140 b may obtain an XR device state, surrounding environmentinformation, user information, etc. The sensor unit 140 b may include aproximity sensor, an illumination sensor, an acceleration sensor, amagnetic sensor, a gyro sensor, an inertial sensor, an RGB sensor, an IRsensor, a fingerprint recognition sensor, an ultrasonic sensor, a lightsensor, a microphone and/or a radar. The power supply unit 140 c maysupply power to the XR device 100 a and include a wired/wirelesscharging circuit, a battery, etc.

For example, the memory unit 130 of the XR device 100 a may includeinformation (e.g., data) needed to generate the XR object (e.g., anAR/VR/MR object). The I/O unit 140 a may receive a command formanipulating the XR device 100 a from a user and the control unit 120may drive the XR device 100 a according to a driving command of a user.For example, when a user desires to watch a film or news through the XRdevice 100 a, the control unit 120 transmits content request informationto another device (e.g., a hand-held device 100 b) or a media serverthrough the communication unit 130. The communication unit 130 maydownload/stream content such as films or news from another device (e.g.,the hand-held device 100 b) or the media server to the memory unit 130.The control unit 120 may control and/or perform procedures such asvideo/image acquisition, (video/image) encoding, and metadatageneration/processing with respect to the content and generate/outputthe XR object based on information about a surrounding space or a realobject obtained through the I/O unit 140 a/sensor unit 140 b.

The XR device 100 a may be wirelessly connected to the hand-held device100 b through the communication unit 110 and the operation of the XRdevice 100 a may be controlled by the hand-held device 100 b. Forexample, the hand-held device 100 b may operate as a controller of theXR device 100 a. To this end, the XR device 100 a may obtain informationabout a 3D position of the hand-held device 100 b and generate andoutput an XR object corresponding to the hand-held device 100 b.

Examples of a Robot Applicable to the Present Disclosure

FIG. 21 illustrates a robot applied to the present disclosure. The robotmay be categorized into an industrial robot, a medical robot, ahousehold robot, a military robot, etc., according to a used purpose orfield.

Referring to FIG. 21 , a robot 100 may include a communication unit 110,a control unit 120, a memory unit 130, an I/O unit 140 a, a sensor unit140 b, and a driving unit 140 c.

The communication unit 110 may transmit and receive signals (e.g.,driving information and control signals) to and from external devicessuch as other wireless devices, other robots, or control servers. Thecontrol unit 120 may perform various operations by controllingconstituent elements of the robot 100. The memory unit 130 may storedata/parameters/programs/code/commands for supporting various functionsof the robot 100. The I/O unit 140 a may obtain information from theexterior of the robot 100 and output information to the exterior of therobot 100. The I/O unit 140 a may include a camera, a microphone, a userinput unit, a display unit, a speaker, and/or a haptic module. Thesensor unit 140 b may obtain internal information of the robot 100,surrounding environment information, user information, etc. The sensorunit 140 b may include a proximity sensor, an illumination sensor, anacceleration sensor, a magnetic sensor, a gyro sensor, an inertialsensor, an IR sensor, a fingerprint recognition sensor, an ultrasonicsensor, a light sensor, a microphone, a radar, etc. The driving unit 140c may perform various physical operations such as movement of robotjoints. In addition, the driving unit 140 c may cause the robot 100 totravel on the road or to fly. The driving unit 140 c may include anactuator, a motor, a wheel, a brake, a propeller, etc.

Example of AI device to which the present disclosure is applied.

FIG. 22 illustrates an AI device applied to the present disclosure. TheAI device may be implemented by a fixed device or a mobile device, suchas a TV, a projector, a smartphone, a PC, a notebook, a digitalbroadcast terminal, a tablet PC, a wearable device, a Set Top Box (STB),a radio, a washing machine, a refrigerator, a digital signage, a robot,a vehicle, etc.

Referring to FIG. 22 , an AI device 100 may include a communication unit110, a control unit 120, a memory unit 130, an I/O unit 140 a/140 b, alearning processor unit 140 c, and a sensor unit 140 d.

The communication unit 110 may transmit and receive wired/radio signals(e.g., sensor information, user input, learning models, or controlsignals) to and from external devices such as other AI devices (e.g.,100 x, 200, or 400 of FIG. 16 ) or an AI server (e.g., 400 of FIG. 16 )using wired/wireless communication technology. To this end, thecommunication unit 110 may transmit information within the memory unit130 to an external device and transmit a signal received from theexternal device to the memory unit 130.

The control unit 120 may determine at least one feasible operation ofthe AI device 100, based on information which is determined or generatedusing a data analysis algorithm or a machine learning algorithm. Thecontrol unit 120 may perform an operation determined by controllingconstituent elements of the AI device 100. For example, the control unit120 may request, search, receive, or use data of the learning processorunit 140 c or the memory unit 130 and control the constituent elementsof the AI device 100 to perform a predicted operation or an operationdetermined to be preferred among at least one feasible operation. Thecontrol unit 120 may collect history information including the operationcontents of the AI device 100 and operation feedback by a user and storethe collected information in the memory unit 130 or the learningprocessor unit 140 c or transmit the collected information to anexternal device such as an AI server (400 of FIG. 16 ). The collectedhistory information may be used to update a learning model.

The memory unit 130 may store data for supporting various functions ofthe AI device 100. For example, the memory unit 130 may store dataobtained from the input unit 140 a, data obtained from the communicationunit 110, output data of the learning processor unit 140 c, and dataobtained from the sensor unit 140. The memory unit 130 may store controlinformation and/or software code needed to operate/drive the controlunit 120.

The input unit 140 a may acquire various types of data from the exteriorof the AI device 100. For example, the input unit 140 a may acquirelearning data for model learning, and input data to which the learningmodel is to be applied. The input unit 140 a may include a camera, amicrophone, and/or a user input unit. The output unit 140 b may generateoutput related to a visual, auditory, or tactile sense. The output unit140 b may include a display unit, a speaker, and/or a haptic module. Thesensing unit 140 may obtain at least one of internal information of theAI device 100, surrounding environment information of the AI device 100,and user information, using various sensors. The sensor unit 140 mayinclude a proximity sensor, an illumination sensor, an accelerationsensor, a magnetic sensor, a gyro sensor, an inertial sensor, an RGBsensor, an IR sensor, a fingerprint recognition sensor, an ultrasonicsensor, a light sensor, a microphone, and/or a radar.

The learning processor unit 140 c may learn a model consisting ofartificial neural networks, using learning data. The learning processorunit 140 c may perform AI processing together with the learningprocessor unit of the AI server (400 of FIG. 16 ). The learningprocessor unit 140 c may process information received from an externaldevice through the communication unit 110 and/or information stored inthe memory unit 130. In addition, an output value of the learningprocessor unit 140 c may be transmitted to the external device throughthe communication unit 110 and may be stored in the memory unit 130.

The above-described embodiments of the present disclosure are applicableto various mobile communication systems.

As is apparent from the foregoing description, according to anembodiment of the present disclosure, even when a UE has a plurality ofPC5 RRC connections and a plurality of PC5 unicast links, a PC5 unicastlink to which RLF has occurred may be accurately identified andreleased.

The above-described embodiments of the present disclosure are applicableto various mobile communication systems.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the disclosures. Thus, itis intended that the present disclosure covers the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of operating a first user equipment (UE)in a wireless communication system, the method comprising: establishingtwo or more PC5 radio resource control (RRC) connections with a secondUE by the first UE; and releasing a PC5 RRC connection for whichsidelink radio link failure (SL RLF) has been declared among the two ormore PC5 RRC connections by the first UE, wherein there is a PC5 unicastlink associated with the PC5 RRC connection, and wherein the PC5 unicastlink for which the SL RLF has been declared and the PC5 RRC connectionhas been released is indicated by a PC5 link identifier (ID), whereinthe PC5 link identifier is provided by an access stratum (AS) layer ofthe first UE to a vehicle-to-everything (V2X) layer of the first UE, andwherein the V2X layer releases the PC5 unicast link indicated by the PC5link identifier.
 2. The method according to claim 1, wherein the firstUE transmits, to a base station (B S), information related to the PC5unicast link for which the SL RLF has been declared and the PC5 RRCconnection has been released.
 3. The method according to claim 2,wherein when another PC5 RRC connection is released for a reason otherthan SL RLF among the two or more PC5 RRC connections, the first UEprovides, to a higher layer, information related to a PC5 unicast linkassociated with the PC5 RRC connection.
 4. The method according to claim1, wherein the PC5 unicast link is related to the PC5 RRC connectionreleased by the SL RLF.
 5. The method according to claim 1, wherein anAS layer of the first UE indicates to a V2X layer of the first UE thatthe PC5 RRC connection has been released based on the SL RLF.
 6. A firstuser equipment (UE) configured to operate in a wireless communicationsystem, the first UE comprising: at least one processor; and at leastone computer memory operatively coupled to the at least one processorand storing instructions which when executed, cause the at least oneprocess to perform operations, wherein the operations comprise:establishing two or more PC5 radio resource control (RRC) connectionswith a second UE by the first UE; and releasing a PC5 RRC connection forwhich sidelink radio link failure (SL RLF) has been declared among thetwo or more PC5 RRC connections by the first UE, wherein there is a PC5unicast link associated with the PC5 RRC connection, and wherein the PC5unicast link for which the SL RLF has been declared and the PC5 RRCconnection has been released is indicated by a PC5 link identifier (ID),wherein the PC5 link identifier is provided by an access stratum (AS)layer of the first UE to a vehicle-to-everything (V2X) layer of thefirst UE, and wherein the V2X layer releases the PC5 unicast linkindicated by the PC5 link identifier.
 7. The first UE according to claim6, wherein the first UE communicates with at least one of another UE, aUE or base station (BS) related to an autonomous driving vehicle, or anetwork.
 8. A processor for performing operations for a user equipment(UE) in a wireless communication system, wherein the operationscomprise: establishing two or more PC5 radio resource control (RRC)connections with a second UE by a first UE; and releasing a PC5 RRCconnection for which sidelink radio link failure (SL RLF) has beendeclared among the two or more PC5 RRC connections by the first UE,wherein there is a PC5 unicast link associated with the PC5 RRCconnection, and wherein the PC5 unicast link for which the SL RLF hasbeen declared and the PC5 RRC connection has been released is indicatedby a PC5 link identifier (ID), wherein the PC5 link identifier isprovided by an access stratum (AS) layer of the first UE to avehicle-to-everything (V2X) layer of the first UE, and wherein the V2Xlayer releases the PC5 unicast link indicated by the PC5 linkidentifier.
 9. A non-transitory computer-readable storage medium storingat least one computer program, the at least one computer programincluding instructions which when executed by at least one processor,cause the at least one processor to perform operations for a UE, whereinthe operations comprise: establishing two or more PC5 radio resourcecontrol (RRC) connections with a second UE by a first UE; and releasinga PC5 RRC connection for which sidelink radio link failure (SL RLF) hasbeen declared among the two or more PC5 RRC connections by the first UE,wherein there is a PC5 unicast link associated with the PC5 RRCconnection, and wherein the PC5 unicast link for which the SL RLF hasbeen declared and the PC5 RRC connection has been released is indicatedby a PC5 link identifier (ID), wherein the PC5 link identifier isprovided by an access stratum (AS) layer of the first UE to avehicle-to-everything (V2X) layer of the first UE, and wherein the V2Xlayer releases the PC5 unicast link indicated by the PC5 linkidentifier.